BEN AND JEN TO WED! thumbnail

Ben Affleck is at the center of a marriage mystery over a half million-dollar ring he bought to pop the question to girlfriend Jennifer Garner.

While Ben publicly denied proposing at the actress’ 33rd birthday party, friends have told The National Enquirer that the actor secretly asked for the Alias star’s hand in marriage – and she said yes.

Ben, 32, was hoping to overwhelm her by flying in family and friends for a backyard surprise party on Saturday, April 16, and then following it up with the biggest, most gorgeous present she’s ever received: a 4.5 carat cushion cut diamond ring.

Ben had the diamond ring specially flown in from Harry Winston jewelers in New York and was planning on packing it in a box within a box within a box. The outside box was so big that Ben would have had to transport it in his pick-up truck.

But a disappointed Ben halted his secret plans when helicopters began flying overhead and photographers started camping outside Jennifer’s home in anticipation of a wedding.

“Ben carefully planned the whole scenario. But word leaked out about a possible wedding and it didn’t go off the way he planned,” said a close source. “He’s wanted to marry her since they began dating eight months ago. So he proposed to Jennifer in secret.

“She was bowled over and said yes to marriage. She’s been wanting this for the longest time.”

The couple met in 2001 on the set of Pearl Harbor and then co-starred in Daredevil. Their relationship took off when Ben appeared in Jennifer’s Elektra sequel last year.

Pals say Ben worked in secret with Jennifer’s assistant to set up the surprise birthday party – and even flew in Jennifer’s friends and family from all over the U.S. To make it the most unforgettable birthday ever, Ben collected the ring from Harry Winston security in Brentwood, Calif., April 15, and then had it engraved at Phillipe’s jewelers. “Afterward Jennifer told Ben how much she loved him and could not have asked for a better birthday,” said the source.

Affleck’s publicist has denied the engagement but the insider insisted: “Ben did still ask Jennifer to marry him and gave her the ring — she said yes.”