The America's Got Talent judge is engaged to Lauren Silverman after proposing on Christmas Eve during a family vacation in Barbados, where they first met. Cowell reportedly popped the question while out on a walk on the beach with Silverman.
Their 7-year-old son, Eric, and Silverman's eldest child, Adam, witnessed the proposal.
"They are both super happy," the source says of the newly engaged couple. "They've been together a long time now and adore each other, so it's not a huge surprise to their close friends."
The newly-engaged couple first met in 2004 at a resort on the Caribbean island. In July 2013, it was revealed that Cowell was expecting his first child with Silverman while she was still legally married to her ex-husband Andrew Silverman, a real estate mogul who had been friends with Cowell. The two finalized their divorce that following December.
"The affair is not something I am proud of or wanted to happen in terms of hurting anyone," he said in an interview a few years ago. "It just happened … But then, of course, you have a baby, and you look at the baby, and you kinda go, 'This is what happened from it.'"
Before Silverman, Cowell dated entertainment journalist Terri Seymour and has been linked to Carmen Electra and pop singer Dannii Minogue.