Jeremy, who reportedly has split from his younger kid's mother Erin Wagner recently after seven years, wrote on Twitter: "Happy Birthday son. Wow 20!," the Mirror reported.
Justin's mother Pattie Mallette, who split from Jeremy when the teenage icon was just two, also tweeted: "Happy Birthday YOU KNOW WHO! I love you. Xoxo"
Meanwhile, Justin just posted a smiley face on his Twitter account.