BLAIR UNDERWOOD was inspired to reprise Raymond Burr’s role as disabled TV detective “Ironside” by his mother – who suffers from multiple sclerosis and is wheelchair-bound.

Marilyn Underwood, 77, has bravely battled the crippling disease since 1997, and a source says her son relied on her advice while playing his physically challenged character.

“Blair has always believed Marilyn is the strongest woman on the planet,” a TV insider told The ENQUIRER.

“Taking on the role of a crime-fighter in a wheelchair is his way of showing his love and pride in the way she’s faced up to MS.”

A former interior decorator, Marilyn lives in Virginia with Underwood’s father Frank, who is her main caregiver.

But the 49-year-old former “L.A. Law” star – who resides in Los Angeles with wife Desiree  DaCosta and their three children – calls or Skypes his mom daily, said the source.

In the updated version of “Ironside,” which originally aired on NBC from 1967 to 1975, Underwood plays a tough-as-nails NYPD cop who chases bad guys after being paralyzed by a gunshot.

And the star apparently got mobility tips from his mom before the pilot went into production.

“She told him, ‘Darling, at one point you just start to think of these wheels as your legs,’” said the source.

“When she viewed a copy of the series’ first episode, her eyes welled with tears of pride.

“His mom is slipping away a little more each day, and Blair’s glad he got this chance to pay tribute to her courage.”