Barbara Bush, daughter of former President George W. Bush and former First Lady Laura Bush, tied the knot with her fiancé, screenwriter Craig Coyne, on Sunday in an intimate secret wedding.

Only 20 family members witnessed the simple yet romantic ceremony, which was held at the Bush family compound in Kennebunkport, Maine, in the backyard overlooking the ocean.

“A very short, sweet ceremony” is how Barbara, 36, described it to PEOPLE.

After Barbara’s father walked her down the aisle, the bride and groom exchanged vows in front of their immediate family, including former President Bush, 72, Mrs. Bush, 71, and Barbara’s grandfather, former President George H.W. Bush, 94. Barbara’s twin sister, Jenna Bush Hager, served as matron of honor, and her daughters, Margaret, 5, and Poppy, 3, were flower girls along with Coyne’s niece, Emma, 5. Poppy did double duty at the ceremony, also serving as the ring bearer.

The bride’s aunt, Dorothy “Doro” Bush Koch, officiated.